During manufacturing of a disk drive, servo sectors are typically written to a disk to define a plurality of evenly-spaced, concentric tracks. Servo writers are typically used to write the servo sectors to the disk during disk drive manufacturing. Servo writers often employ extremely accurate head positioning mechanics, such as laser interferometers or optical encoders, to ensure that the servo sectors are written at the proper radial location, typically, from the inner diameter of the disk to the outer diameter of the disk. In addition, extremely accurate clocking systems may be utilized in order to write the servo sectors in the proper circumferential locations on the disk. Alternatively, instead of utilizing a servo writer, disk drives may perform self servo-writing in which the disk drive itself writes the servo sectors to the disk.
Referring to FIG. 1A, an external servo writer 130 may be used for writing spiral reference patterns 1360-1367 (FIG. 1B) to a disk 116 of a disk drive 118. The spiral reference patterns (servo spiral seeds) may include reference servo bursts that can be used for forming product servo bursts. The disk drive 118 comprises control circuitry 120 and a head disk assembly (HDA) 122. The HDA comprises the disk 116, an actuator arm 124, a head 126 connected to a distal end of the actuator arm 124, and a voice coil motor 128 for rotating the actuator arm 124 about a pivot to position the head 126 radially over the disk 116. The external spiral servo writer 130 may be used to control a radial location of the head 126 for writing a plurality of the spiral reference patterns 1360-1367 between an inner radial location 131 and an outer radial location 132.
A head positioning pin 133 of the external spiral servo writer 130 may be inserted into the HDA 122 before writing the spiral reference patterns. The head positioning pin 133 may be used for engaging the actuator arm 124. The external spiral servo writer 130 comprises head positioning mechanics 134 used to derive a radial location of the head 126. The head positioning pin 133 is actuated in response to the radial location of the head 126 in a closed loop system in order to position the head 126 radially over the disk 116 while writing a plurality of reference servo bursts to the disk along a plurality of substantially spiral paths to form the plurality of spiral reference patterns 1360-1367 as illustrated in FIG. 1B.
During the servo-writing of servo spiral seeds and/or other servo information to a disk, a nominal pre-determined stroke is typically used to write the servo information across the disk. The nominal stroke is usually pre-determined for a class of disk drives in order to prevent the writing of servo information too close to a ramp of the disk drive. By utilizing a pre-determined nominal stroke, the full area of each particular disk may not be utilized for writing servo information and defining the tracks of the disk drive. Accordingly, what is needed are apparatus and methods to accurately detect a ramp position relative to a disk in order to produce a customized servo write stroke to maximize the use of the area of the disk.